Place Painters tape on front/center of t-shirt to make a 3 inch wide stripe. Make sure the tape is pressed firmly down on the t-shirt. You can measure it out if you wish, I just eyeballed it.

Place wax paper inside the shirt so the paint does not bleed through to the back of the shirt. Paint inside the blue tape. Make sure to place the paint on evenly for best results.

Last paint the the collar of the shirt and the edges of the sleeves. I used the hem lines as my border lines. Make sure to place wax paper in the sleeves and neck. Let dry, turn over and do the back of the neck and sleeves. Refer to pictures.

For PantsYou can purchase green pants at the thrift store. Another option is to dye an old pair of khaki pants green. You can purchase green fabric dye at most craft stores.

For the WatchWe already had the toy watch so I didn't have to make anything. However, if you don't want to go out and buy one I recommend drawing one on the child's wrist with face paints.

If you need more inspiration, here's the link to the Ben 10 theme song, click here.

My nephew is crazy about Ben 10- here he is in his 'four arms' costume:http://www.flickr.com/photos/crunchcandy/2873564204/I didn't have a clue who Ben 10 was until last weekend when my nephew turned 5 and every single gift he got was Ben 10 related!

Thank you so much. My son is 4 and we have everything set for Halloween except the shirt. I bought a thick white t-shirt and was just going to wing it by sewing the collar, cuffs & strip down the middle, but this will help so much!

Thanks for the great tips and directions! My 8 year old wanted to be Ben 10, and your directions were just what I needed! I bought him a pair of Tony Hawk (his favorite) pants and painted a white t-shirt that I purchased at Michael's for $2.50. I used a paper bag since I was out of wax paper. Also, I used black acrylic paint (it said it was safe for fabric), but I haven't tried to wash it. It was a great hit at school and trick-or-treating last night! Thanks again!

The shirt (painted with acrylic paint) washed fine the first time on a delicate cycle, but the second time I did a regular cycle. That lightened the black a bit.

My son had a Ben 10 party yesterday, and I had trouble finding someone to make a cake for the party. I didn't want the standard copy from a plate or napkin. When I was at Costco, I noticed they had a skateboard cake with a boy on the skateboard, so I asked if they could make the cake without the skateboard. They did more than that! She made the black and white shirt, green pants, omnitrix, and even got the hair right!

my boyfriend is obsseded with ben 10 and he is 16 and i wanted to get him the costume ofr his birthday but you cant buy it anywhere for adults so now i will make it for him thank you very much really big help!xox

My son wanted to be Ben 10 for his school fancy dress competition, he's a ben 10 freak. So I was worried if I will be able to get a costume. And then I came across ur easy and helpful instruction. And now i have made a t shirt for him and purchased a green cargos. He's excited and so am I! Thanks.

I wish I saw this earlier then I would've saved lots of money. Now, my sons want Ben 10 shirts and tomorrow I'm going to get plain white shirts and get down to work..:). Thanks alot for sharing this..^_^

this is waaaaaay easier than the other suggestions i looked up! thanks for the tips! i made the ben 10 ultimate alien ben costume (green jacket)for my older son. can't wait to surprise them with the costumes for halloween!

Another thank you :), I'm looking forward to making my 5 yr old son's request now!

Also, fyi, I found this post on this website and, well, it's pretty much a straight copy of yours, minus the pictures showing how YOU actually did it...http://www.infobarrel.com/How_To_Make_A_Ben_10_Costume#axzz1aoG0OD5M